Liquid crystal device for direct display of analog information

ABSTRACT

A liquid crystal device for direct display of analog information in images and patterns includes a layer of liquid crystal material sandwiched between a front and a back transparent plate. Transparent conducting films are applied to selected portions of the sides of both front and back transparent plates adjacent to the liquid material. A resistor network is provided electrically continuous with at least one of the transparent conducting films for impressing a voltage gradient transversely across the transparent conducting films so as to permit the selective, incremental reorientation of the liquid crystal material into the desired images and patterns.

BACKGROUND OF THE INVENTION

The present invention relates generally to liquid crystal displays. Morespecifically, this invention relates to a liquid crystal display inwhich analog information may be presented in other than alphanumericmanner and the interfacing by which the display is controlled is greatlyminimized or eliminated.

As is well known, liquid crystal displays are electrically controlleddevices utilizing the optical properties of liquid crystal materials todisplay desired patterns with only ambient light. Most commercial liquidcrystal displays, and all of the so called "light-shutter" type liquidcrystal displays discussed hereinafter, employ liquid crystal materialshaving a twisted nematic molecular orientation in the absence of anelectric field. Such displays utilize principally one of two basicmechanisms by which light passing therethrough is controlled. In"field-effect" cells the presence of an electric field changes thedirection of the liquid crystal material's optic axis. In "scattering"cells the presence of an electric field results in either intense lightscattering due to a disruption in the ordered, unenergized molecularstructure ("dynamic scattering") or an intense light focusing due to anordering of the unordered, unenergized molecular structure ("quiescentscattering"). As a result of greater power requirements and slowerresponse time of scattering cells, field-effect cells are greatlypreferred in nearly all present day applications.

Presently nearly all liquid crystal displays are utilized to form fixedformat, alphanumeric patterns. These displays are digital in nature,having a plurality of physically and electrically discrete, separatelyaddressed, pattern segments. Such patterns require multiple-leadinterfacing with generally costly, complex and physically large drivingnetworks in order to effectuate the desired characters.

Perhaps the best known example of alphanumeric liquid crystal displaysare those of the field-effect, light-shutter type in which a layer ofnematic liquid crystal material is sandwiched between transparentparallel plates. A 90° twist is induced in the nematic liquid crystalmaterial by rubbing the plates at right angles to each other. Polarizersare placed adjacent to the outer surface of both plates such that whenan electric field of sufficient potential is impressed acrosstransparent conducting films applied to the inner surfaces of bothplates, the nematic structure will untwist and the display will changefrom a light transmitting to an opaque medium or vice versa, dependingupon the orientation of the two polarizers, thereby producing theaforesaid light-shutter effect. Typically the front plate conductingfilm is constructed with a plurality of physically and electricallyseparate conducting regions which, when appropriately, selectivelyenergized, leave other regions unaffected so as to produce the desiredletter or numeral.

Although some field-effect cells have attempted to display images orsymbols other than letters or numerals, such liquid crystal displayshave without exception required driving networks to appropriatelycontrol what quickly becomes a phenomenal number of separate conductingregions. Moreover, the greatly increased complexity of these networksover those associated with conventional alphanumeric display patternshas resulted in costly display controls frequently too large for mostapplications.

In much the same manner, the less desirable "scattering" type cells havealso been utilized to form alphanumeric patterns. I am aware of only oneinstance in which general images or symbols other than letters ornumerals have been formed with "scattering" type cells. In an articleentitled "A Electronically Scanned Analog Liquid Crystal Display"published in Volume 9 Applied Optics, on pages 1323-1329 (June, 1970),the author, R. A. Soref, disclosed a technique for use with "scattering"type liquid crystal cells in which voltage gradients are inducedtransversely across the transparent conducting films so that the desiredpatterns can be formed. Although this technique does not require the useof the conventional driving networks previously noted, neverthelessdriving equipment of a differeing type, including at least two voltagewaveform generators external to the display, are required to effectuateeven the simplest of patterns. The quantity of voltage generators, aswell as the complexity of the voltage waveforms required, increases withthe complexity of the desired pattern, likely resulting in an even morecostly, complex, and a physically large display than needed forfield-effect liquid crystal displays having similar patterns.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to provide a liquid crystaldevice for direct display of analog information in images and patternsof other than an alphanumeric character.

It is another object of the invention to provide a liquid crystal devicefor direct display of analog information, as above, in which the needfor external driving and/or controlling circuitry is mimimized oreliminated.

It is still another object of the invention to provide a liquid crystaldevice for direct display of analog information, as above, in whichanalog information may be directly displayed without the need forindividually, selectively energizing separate conducting regions on thefront transparent plate of the device.

It is yet another object of the invention to provide a liquid crystaldevice for the direct display of analog information, as above, in whichthe analog information may be directly displayed by including in atleast one of the transparent conducting films at least two physicallyseparate, distinct segments and impressing a voltage gradienttransversly across such segments.

It is a further object of the invention to provide a liquid crystaldevice for direct display of analog information, as above, in which theaforesaid voltage gradient is produced by a resistor network.

It is still a further object of the invention to provide a liquidcrystal device for direct display of analog information, as above, inwhich the resistor network is integrally formed with the transparentconducting film and is electrically continuous with all of thetransparent conducting film segments.

It is yet a further object of the invention to provide a liquid crystaldevice for direct display of analog information, as above, in which theratio of resistances within the resistor network may be either linear ornon-linear such that any non-linear signal or information may be offsetthereby and a direct and linear display of such information effectuated.

It is an additional object of the invention to provide a liquid crystaldevice for direct display of analog information, as above, in which theonly required input to the device is the information signal to bedisplayed, the power required to operate the device being supplied bysuch information signal.

These and other objects and advantages of the present invention overexisting prior art forms will become more apparent and fully understoodfrom the following description in conjunction with the accompanyingdrawings.

In general, a device embodying the concept of the present inventionincludes a liquid crystal device for direct display of analoginformation in images and patterns. The device includes a layer ofliquid crystal material sandwiched between a front and a backtransparent plates. Transparent conducting means are applied to selectedportions of the sides of both front and back transparent plate adjacentto the liquid material. Means are provided electrically continuous withat least one of the transparent conducting means for impressing avoltage gradient transversely across the transparent conducting means soas to permit the selective, incremental reorientation of the liquidcrystal material into the desired images and patterns.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded, perspective view of a liquid crystal displayembodying the concept of the present invention and depictingparticularly a three terminal, linear, equal-value resistor network;

FIG. 2 is an elevational view of another embodiment of the liquidcrystal display according to the present invention depictingparticularly a two terminal, non-linear, unequal-value resistor network;

FIG. 3 is a schematic diagram of the liquid crystal display illustratedin FIG. 1; and

FIG. 4 is a schematic diagram of the liquid crystal display illustratedin FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1 of the drawings, a liquid crystal device fordirect display of analog information is illustrated generally by thenumeral 10. In this particular embodiment the liquid device 10 includesfront and back transparent plates 11 and 12 respectively, made of anelectrically non-conducting material such as glass or the like. Plates11 and 12 are separated by gasket 13 which together with plates 11 and12 collectively define the narrow chamber for encapsulating a thin filmof liquid crystal material 14. Although liquid crystal material 14 ispreferrably of twisted nematic molecular orientation, it should be notedthat the present invention is suitable for use with liquid crystalmaterial having any type of molecular orientation. Futhermore, althoughit must again be understood that the concept of the present invention isnot limited thereto, in the event that the present invention is to beembodied within a "light-shutter" type of liquid crystal display cell,conventional front and back polarizers 15 and 16, respectively, may beapplied by any suitable means such as transparent epoxy to the sides ofplates 11 and 12, respectively, opposite that constraining liquidcrystal material 14, hereinafter referred to as the "outer side".Similarly, in the event that the display is to be viewed with ambientlighting passing into the display from the front, a reflector 17 whichforward scatters the polarized light without depolarizing the same maybe applied to the back side of the back polarizer 16.

As shown in FIG. 1, and schematically depicted in FIG. 3, patterns oftransparent conducting material such as tin oxide or indium oxide areformed on or applied to the side of both front and back transparentplates adjacent to liquid crystal material 14, hereinafter referred toas the "inner sides", by any of numerous conventional means such asphotoresist etching, sputtering, or the like and are indicated generallyby the numerals 20 and 21, respectively. Transparent conducting material20 is formed into a plurality of physically discrete, rectangularsegments indicated generally by the numeral 22 and specifically as 22Athrough 22J. The exact quantity of segments 22 may be varied as desired,being limited primarily by the voltage range of the external voltagesignals with which liquid crystal device 10 is designed to operate andsecondarily by the threshold voltage of liquid crystal material 14. Thelongitudinally outermost of these rectangular segments (22A and 22J) areconnected through conducting strips 23, 24 extending to the bottom edgeof plate 11 to an external voltage signal (not shown) discussedhereinafter. Front transparent plate 11 extends beneath the remainingportions of the liquid crystal device 10 so that a suitable electricalconnector can engage the lower portion of plate 11 to connect conductingstrips 23, 24 and other conducting strips to be indicated hereinafter tothe various external voltage signals, which may be either AC or DC,hereinafter described in more detail.

A linear resistor network, indicated generally by the numeral 25, mayalso be formed out of transparent conducting material 20. A resistor(e.g., 25A) is interposed between each two segments, (e.g., 22A and 22B)resulting in nine resistors 25A through 25I. Each resistor 25A through25I preferrably follows a stylized serpentine path. Not only does such adesign permit greater resistance values due to the greater length andnarrower width of transparent conducting material 20 between eachsegment (although as will be explained hereinafter the absolute value ofeach resistor is not of primary significance) but also permits greaterheat dissipation which can in turn substantially improve the coldweather operation of the device. However, as will be emphasizedhereinafter, any desired patterns of display segments and resistors arepermissible.

Transparent conducting material 21 is formed by similar techniques intoa generally rectangular conducting back plate 26 having at least one,but permissibly two conducting strips 27, 28 for connection to theexternal voltage signal (not shown) as discussed hereinafter. Regardlessof the segment pattern 22 utilized it should be noted that the patternlocation of conducting back plate 26 should generally correspond to thatof the entire segment pattern on front plate 11 so that only the liquidcrystal material 14 between segments 22 and conducting back plate 26will ever be exposed to an electric field; in no event should conductingback plate 26 align with any portion of resistor network 25 when plates11 and 12 are bonded to opposite sides of gasket 13. In order tofacilitate external connection with a single connector as previouslydescribed, holes 30 may be made in gasket 13 and filled with anelectrically conducting epoxy material or the like so as to permitelectrical connection between back plate conducting strips 27, 28 andconducting strips 31, 32 respectively.

Having described the construction of liquid crystal device 10, itsoperation as a liquid crystal device for direct display of analoginformation may now be detailed. Referring particularly to FIG. 3,operation of liquid crystal device 10 may be best understood by thefollowing example.

Assume one is desirous of displaying the value of an analog signal suchas the voltage from a conventional motor vehicle fuel tank indicator inwhich a nine volt potential represents a full tank and a zero voltpotential represents an empty tank. A constant potential of nine voltsis first impressed across conducting strips 23 and 24. The nine (9)equal-value resistors 25 will act as an equal voltage divider network,providing a nine volt potential on segment 22A, an eight volt potentialon segment 22B, and so on until a zero volt potential is reached onsegment 22J.

Next, the analog signal from the fuel tank indicator is connected toconducting back plate 26 through conducting strips 31 and/or 32. Merelyfor purposes of the present discussion, assume that the liquid crystalmaterial 14 utilized has a threshold potential of one volt (i.e., whenat least a one volt potential difference is impressed between a segment22 and conducting back plate 26 that segment 22 will turn either "on" or"off" with respect to the remaining unenergized portions of displaydepending on the orientation of polarizers 15 and 16). When the tank isfull and a nine volt potential is impressed on conducting back plate 26it therefor should be readily apparent that only segment 22A will haveless than a one volt potential difference between it and conducting backplate 26. Thus, segment 22A, which in this state may be referred to asthe "null segment," will behave optically opposite that of all othersegments 22. As the voltage from the fuel tank decreases, the "nullsegment" will move steadily toward segment 22J in discrete, one voltincrements. Of course, in the event that the potential on conductingback plate 26 falls outside the potential impressed between conductingstrips 23 and 24, all segments will be either "on" or "off" (i.e., therewill be no "null segment") as all segments will be either above or belowthe threshold voltage.

Several factors should now become readily apparent to one skilled in theart. First, the absolute value of each resistor in the network isimmaterial; only its relative value (or ratio) to each other resistor inthe network is of any consequence, as it is this relationship whichdetermines the potential division between segments and theircorresponding optical response characteristics. Thus, notwithstandinggreat variations in resistances of transparent conducting material fromdisplay to display, as the absolute value of each resistor isimmaterial, it should also be clear highly accurate and precise analogsignal responding liquid crystal displays can be effectuated by merelyaccurately and precisely controlling the surface area of each resistorwith respect to each other resistor in the network. Moreover, asdiscussed further hereinafter, displays can be manufactured at minimalcosts to appropriately respond to an endless variety of analog inputsignals--be they linear or non-linear. Finally, the power dissipated bythe resistor network, by appropriate design, may be utilized tosignificantly extend the lowest permissible operating temperature ofliquid crystal device 10.

The second factor which should now be clear to the skilled artisanactually concerns the manner in which potentials are applied to segments22 and conducting back plate 26. As the potential applied acrossconducting strips 23 and 24 (V₂₃₋₂₄ hereinafter) decreases, the "width"of the "null segment" will increase, all else being equal. In theexample above, if V₂₃₋₂₄ is halved (to 4.5 volts) the "null segment"will consist of two (2) segments 22[(specifically, where the conductingback plate 26 potential (V_(BP) hereinafter) is nine volts, bothsegments 22A and 22B will "null")]. Taking this observation in a broadercontext leads to the important point that involves recognition of thefact liquid crystal device 10 is, electrically speaking, what is knownin the art as a three-port device, i.e., it has three terminals forexternal connection. Thus, there are at least three permutations ofvoltage-potential applications that are of interest in this embodiment:where V₂₃₋₂₄ is fixed and V_(BP) is variable (illustrated hereinabove);where V₂₃₋₂₄ is variable and V_(BP) is fixed; and where both V₂₃₋₂₄ andV_(BP) are variable, either independently or in some related manner. Ofcourse, by appropriate design of resistor network 22 liquid crystaldevice 10 may be made to have almost any number of terminals (i.e., be a"N-port" device) for acceptance of a similar number of analog signals.Here again the skilled artisan would find all such variations andmodifications highly useful in producing liquid crystal devices suitablefor direct response to almost any highly complex analog signal one isdesirous of displaying and should therefore be taken to be within thespirit of the present invention.

A third factor which should now be plainly evident involves theformation of physically discrete, rectangular segments 22 out oftransparent conducting material 20. Where transparent conductingmaterial 20 formed into a single continuous plane, impressing acontinuous voltage gradient transversely across such plane would resultin areas of liquid crystal material 14 so close to its thresholdpotential that optically non-definitive regions would exist. Aseparation of transparent conducting material 20 into physicallydistinct segments 22 substantially eliminates these so-called"fringe-effect" regions, providing a highly defined interface betweenoptically opposite areas of liquid crystal device 10.

An exemplary and useful modification suggested in conjunction with thesecond factor hereinabove involves the case in which V₂₃₋₂₄ and V_(BP)are both variable but in a related manner. Referring to FIGS. 1 and 2,conducting strips 31, 32 are connected with conducting strips 23, 24respectively, through two resistors (not shown) which may be eitherexternal to liquid crystal device 10 or formed from transparentconducting material 20 in a manner similar to resistors 25. If boththese resistors have equal resistances (regardless of what that may be)the potential applied to conducting back plate 26 will always be onehalf the potential applied across conducting strips 23, 24 (i.e., V_(BP)=(1/2)V₂₃₋₂₄).

The desired analog input signal is applied across conducting strips 23,24. Because of the equal-value resistor network, when the analog inputsignal is high in potential a "null segment" will occur in the centerdisplay segment. Thus, a liquid crystal device 10 operating in thismanner should preferrably have an odd number of segments where it isdesired that at least one segment be energized for all possible analoginput signal potentials. As the potential of the analog input signaldecreases, the "width" of the "null segment" will expand outwardly,simultaneously toward segments 22A and 22J in a manner similar to thatof an opening cat's eyelids. Varying the ratio of resistances of the tworesistors between conducting strips 31, 32 and conducting strips 23, 24,respectively, will shift the initial "null segment" to the right or leftdepending on which resistor has the greater (or conversely smaller)resistance.

Turning to FIG. 2, illustrated therein is a second embodiment of thepresent invention, differing from the embodiment depicted in FIG. 1 inonly two respects: First, this embodiment incorporates a non-linearresistor network in which the relative value of each resistor increasesfrom segments 25A to 25I (i.e., R_(25A) >R_(25B) >R_(25C) . . .>R_(25I)). The second variance involves the conversion of the three-portdevice of FIG. 1 into a two-port device by the elimination of conductingstrip 23 and inclusion of another resistor 33 in the pattern oftransparent conducting material 20, connected between segment 22A andconducting strip 31. Conducting strip 32 (the electrical equivalent toconducting strip 31) has also been eliminated.

The operation of this embodiment is best understood by reference to theelectrical schematic diagram in FIG. 4. Merely for purposes ofdiscussion we shall assume the threshold potential of the liquid crystalmaterial 14 utilized in this embodiment is three volts and thatconducting strip 31 is maintained at "ground" potential (zero volts withrespect to all other points in liquid crystal device 10). The analogsignal to be displayed is applied to conducting strip 24. As thepotential applied to conducting strip 24 exceeds the threshold potentialof three volts, segment 22J will turn "on" ("on" shall for conveniencemerely be taken to designate an optical state opposite that of theremaining, unenergized segments 22). As the potential applied toconducting strip 24 increases further, while segment 22J remains onsegments 22I to 22A will sequentially turn, and remain, on. Thus,segments 22 will turn on from right to left in a fashion similar to thatof a thermometer in which the liquid encapsulated therein continuallyrises with temperature.

Resistor 33 is necessary to provide a sufficient potential differencebetween segment 22A and conducting back plate 26 so that segment 22A mayturn on. Where desired, resistor 33 may additionally function as a"loading" resistor, absorbing any possible transient voltage spikes thatmay occur in the analog input signal.

Since the total resistance to any particular segment 22 increases as oneproceeds from segment 22J through the resistor network toward segment22A, in order to insure that an equal and linear voltage drop(preferrably equal to the threshold potential) occurs across eachsegment, the incremental resistance between each segment mustproportionally decrease as one proceeds nearer to segment 22A. Thus, anon-linear, analog input signal can be directly displayed by a linearlyexpanding "null segment" through the proper selection of the resistanceratio between resistors 25 so as to offset the non-linearity in theanalog input signal.

Inasmuch as the present invention is subject to many variations,modifications and changes in detail, a number of which have beenexpressly stated herein, it is intended that all matter describedthroughout this entire specification or shown in the eaccompanyingdrawings be interpreted as illustrative and not in a limiting sense. Itshould thus be evident that a device constructed according to theconcept of the present invention, and reasonably equivalent thereto,will accomplish the objects of the present invention and otherwisesubstantially improve the art of displaying analog information in liquidcrystal devices.

What is claimed is:
 1. A liquid crystal device for the display of analoginformation in images and patterns and whose operational power isfurnished by a signal containing the analog information, comprising:afront and a back transparent plate, a layer of liquid crystal materialsandwiched between said front and back transparent plates, transparentconducting means applied to selected portions of the side of both saidfront and back transparent plates adjacent said liquid crystal materialincluding at least two physically separate, distinct segments applied toone said transparent plate and at least one conducting plate applied tothe opposite said transparent plate, means for having a voltage gradientimpressed transversely across said transparent plate on which saiddistinct segments are applied including a resistor network formed out ofthe same material utilized to form said distinct segments and located onsaid transparent plate on which said distinct segments are applied, saidresistor network having at least one physically separate, distinctresistor interposed between each said distinct segment such that saidliquid crystal device has only two terminals, and resistor means formedout of the same material utilized to form said distinct segments andconnected between one end of said resistor network and said conductingplate, the signal containing the analog information connected to saidtwo terminals, such that the operational power of the device isfurnished by the signal containing the analog information.
 2. A liquidcrystal device, as defined in claim 1, wherein said liquid crystalmaterial has a twisted nematic structure and primarily field-effectelectrooptic properties and further including means for polarizing lightpassing through said transparent plates and said layer of liquid crystalmaterial.
 3. A liquid crystal device, as defined in claim 2, furthercomprising means adjacent one of said transparent plates for reflectingpolarized light which has passed through said layer of liquid crystalmaterial back through said layer of liquid crystal material withoutdepolarizing said light.
 4. A liquid crystal device, as defined in claim3, wherein said transparent conducting means is selected from the groupconsisting of indium oxide and tin oxide.
 5. A liquid crystal device, asdefined in claim 1, further comprising means adjacent one of saidtransparent plates for reflecting polarized light which has passedthrough said layer of liquid crystal material back through said layer ofliquid crystal material without depolarizing said light.
 6. A liquidcrystal device, as defined in claim 5, wherein said transparentconducting means is selected from the group consisting of indium oxideand tin oxide.
 7. A liquid crystal device, as defined in claim 1,wherein said segments are generally rectangular in shape.
 8. A liquidcrystal device, as defined in claim 7, wherein said resistor network islinear.
 9. A liquid crystal device, as defined in claim 7, wherein saidresistor network is non-linear.